A variety of implantable medical devices (IMDs) for delivering a therapy, monitoring a physiological condition of a patient or a combination thereof have been clinically implanted or proposed for clinical implantation in patients. Some IMDs may employ one or more elongated electrical leads carrying stimulation electrodes, sense electrodes, and/or other sensors. Other IMDs may incorporate electrodes and/or other sensors along or within a housing of the IMD that encloses circuitry and electronic components of the IMD.
IMDs may deliver therapy to and/or monitor conditions of a variety of organs, nerves, muscle or tissue, such as the heart, brain, stomach, spinal cord, pelvic floor, or the like. Some IMDs, such as cardiac pacemakers, monitor a patient's heart activity and provide therapeutic electrical stimulation to the heart of the patient via electrodes coupled to the pacemaker. The electrical stimulation provided by the IMD may include signals such as pacing pulses to address abnormal cardiac rhythms such as bradycardia, tachycardia and fibrillation.
An IMD may sense signals representative of intrinsic depolarizations of the heart and analyze the sensed signals to identify normal or abnormal rhythms. For example, the IMD may sense R-waves attendant to the depolarization of the ventricles of the heart and detect a ventricular tachyarrhythmia based on an analysis of the R-waves. Upon detection of an abnormal rhythm, the IMD may deliver an appropriate electrical stimulation signal or signals to restore or maintain a more normal rhythm. For example, an IMD may deliver bradycardia pacing, ATP, and/or cardioversion or defibrillation shocks to the heart upon detecting an abnormal rhythm.